The present invention relates generally to mitochondria protecting agents for treating diseases in which mitochondrial dysfunction leads to tissue degeneration and, more specifically, to compounds, compositions and methods for treating such diseases.
Mitochondria are the subcellular organelles that manufacture essential adenosine triphosphate (ATP) by oxidative phosphorylation. A number of degenerative diseases may be caused by or associated with either direct or indirect alterations in mitochondrial function. These include Alzheimer""s Disease, diabetes mellitus, Parkinson""s Disease, neuronal and cardiac ischemia, Huntington""s disease and other related polyglutamine diseases (spinalbulbar muscular atrophy, Machado-Joseph disease (SCA-3), dentatorubro-pallidoluysian atrophy (DRPLA) and spinocerebellar ataxias 1, 2 and 6), dystonia, Leber""s hereditary optic neuropathy, schizophrenia, and myodegenerative disorders such as xe2x80x9cmitochondrial encephalopathy, lactic acidosis, and strokexe2x80x9d (MELAS), and xe2x80x9cmyoclonic epilepsy ragged red fiber syndromexe2x80x9d (MERRF).
Defective mitochondrial activity, including but not limited to failure at any step of the elaborate multi-complex mitochondrial assembly, known as the electron transport chain (ETC), may result in 1) decreases in ATP production, 2) increases in the generation of highly reactive free radicals (e.g., superoxide, peroxynitrite and hydroxyl radicals, and hydrogen peroxide), 3) disturbances in intracellular calcium homeostasis and/or 4) release of apoptosis inducing factors such as, e.g., cytochrome c. Because of these biochemical changes, mitochondrial dysfunction has the potential to cause widespread damage to cells and tissues For example, oxygen free radical induced lipid peroxidation is a well established pathogenetic mechanism in central nervous system (CNS) injury such as that found in a number of degenerative diseases, and in ischemia (i.e., stroke).
Mitochondrial dysfunction also is thought to be critical in the cascade of events leading to apoptosis in various cell types (Kroemer et al., FASEB J. 9:1277-1287, 1995). Altered mitochondrial physiology may be among the earliest events in apoptosis (Zamzami et al., J. Exp. Med. 182:367-377, 1995, Zamzami et al., J. Exp. Med. 181:1661-1672, 1995. In several cell types, including neurons, reduction in the mitochondrial membrane potential (xcex94xcexa8m), a sign of mitochondrial dysfunction, precedes the nuclear DNA degradation that accompanies apoptosis. In cell-free systems, mitochondrial, but not nuclear, enriched fractions are capable of inducing nuclear apoptosis (Newmeyer et al., Cell 70:353-364, 1994). Perturbation of mitochondrial respiratory activity leading to altered cellular metabolic states may occur in mitochondria associated diseases and may further induce pathogenetic events via apoptotic mechanisms. For example, altered mitochondrial activity may lead to undesirable elevated levels of intracellular reactive oxygen species (ROS) and subsequent intracellular damage or cell death.
Stressed (e.g., stressors included free radicals, high intracellular calcium, loss of ATP, among others) mitochondria may release pre-formed soluble factors that can initiate apoptosis through an interaction with novel apoptosomes (Marchetti et al., Cancer Res. 56:2033-2038, 1996; Li et al., Cell 91:479-489, 1997). Release of preformed soluble factors by stressed mitochondria, like cytochrome c, may occur as a consequence of a number events. In some cases, release of apoptotic molecules (apoptogens) occurs when mitochondria undergo a sudden change in permeability to cytosolic solutes under 1.5 KDa. This process has been termed permeability xe2x80x9ctransitionxe2x80x9d. In other cases, the permeability may be more subtle and perhaps more localized to restricted regions of a mitochondrion. In still other cases, overt permeability transition may not occur but apoptogens can still be released as a consequence of mitochondrial abnormalities. Thus, changes in mitochondrial physiology may be important mediators of apoptosis. To the extent that apoptotic cell death is a prominent feature of degenerative diseases, mitochondrial dysfunction may be a critical factor in disease progression.
Diabetes mellitus is a common, degenerative disease affecting 5 to 10 percent of the population in developed countries. The propensity for developing diabetes mellitus is reportedly maternally inherited, suggesting a mitochondrial genetic involvement (Alcolado et al., Br. Med. J. 302:1178-1180, 1991; Reny, International J. Epidem. 23:886-890, 1994). Diabetes is a heterogeneous disorder with a strong genetic component; monozygotic twins are highly concordant and there is a high incidence of the disease among first degree relatives of affected individuals.
At the cellular level, the degenerative phenotype that may be characteristic of late onset diabetes mellitus includes indicators of altered mitochondrial respiratory function, for example impaired insulin secretion and responsivity, decreased ATP synthesis and increased levels of reactive oxygen species. Studies have shown that diabetes mellitus may be preceded by or associated with certain related disorders. For example, it is estimated that forty million individuals in the U.S. suffer from late onset impaired glucose tolerance (IGT). IGT patients fail to respond to glucose with increased insulin secretion. A small percentage (5-10%) of IGT individuals progress to insulin deficient non-insulin dependent diabetes (NIDDM) each year. Some of these individuals further progress to insulin dependent diabetes mellitus (IDDM). These forms of diabetes mellitus, NIDDM and IDDM, are associated with decreased release of insulin by pancreatic beta cells and/or a decreased end-organ response to insulin. Other symptoms of diabetes mellitus and conditions that precede or are associated with diabetes mellitus include obesity, vascular pathologies, peripheral and sensory neuropathies, blindness and deafness.
Due to the strong genetic component of diabetes mellitus, the nuclear genome has been the main focus of the search for causative genetic mutations. However, despite intense effort, nuclear genes that segregate with diabetes mellitus are known only for rare mutations in the insulin gene, the insulin receptor gene, the adenosine deaminase gene and the glucokinase gene. Accordingly, mitochondrial defects, which may include but need not be limited to defects related to the discrete non-nuclear mitochondrial genome that resides in mitochondrial DNA, may contribute significantly to the pathogenesis of diabetes mellitus.
Parkinson""s disease (PD) is a progressive, mitochondria associated neurodegenerative disorder characterized by the loss and/or atrophy of dopamine-containing neurons in the pars compacta of the substantia nigra of the brain. Like Alzheimer""s Disease (AD), PD also afflicts the elderly. It is characterized by bradykinesia (slow movement), rigidity and a resting tremor. Although L-Dopa treatment reduces tremors in most patients for a while, ultimately the tremors become more and more uncontrollable, making it difficult or impossible for patients to even feed themselves or meet their own basic hygiene needs.
It has been shown that the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces parkinsonism in animals and man, at least in part through its effects on mitochondria. MPTP is converted to its active metabolite, MPP+, in dopamine neurons; it then becomes concentrated in the mitochondria. The MPP+ then selectively inhibits the mitochondrial enzyme NADH:ubiquinone oxidoreductase (xe2x80x9cComplex Ixe2x80x9d), leading to the increased production of free radicals, reduced production of adenosine triphosphate and, ultimately, the death of affected dopamine neurons.
Mitochondrial Complex I is composed of 40-50 subunits; most are encoded by the nuclear genome and seven by the mitochondrial genome. Since parkinsonism may be induced by exposure to mitochondrial toxins that affect Complex I activity, it appears likely that defects in Complex I proteins may contribute to the pathogenesis of PD by causing a similar biochemical deficiency in Complex I activity. Indeed, defects in mitochondrial Complex I activity have been reported in the blood and brain of PD patients (Parker et al., Am. J. NeuroL. 26:719-723, 1989).
Similar theories have been advanced for analogous relationships between mitochondrial defects and other neurological diseases, including Alzheimer""s disease (AD), Leber""s hereditary optic neuropathy, schizophrenia, xe2x80x9cmitochondrial encephalopathy, lactic acidosis, and strokexe2x80x9d (MELAS), and xe2x80x9cmyoclonic epilepsy ragged red fiber syndromexe2x80x9d (MERRF).
For example, AD is a progressive neurodegenerative disorder that is characterized by loss and/or atrophy of neurons in discrete regions of the brain, and that is accompanied by extracellular deposits of xcex2-amyloid and the intracellular accumulation of neurofibrillary tangles. It is a uniquely human disease, affecting over 13 million people worldwide. It is also a uniquely tragic disease. Many individuals who have lived normal, productive lives are slowly stricken with AD as they grow older, and the disease gradually robs them of their memory and other mental faculties. Eventually, they cease to recognize family and loved ones, and they often require continuous care until their eventual death.
There is evidence that defects in oxidative phosphorylation within the mitochondria are at least a partial cause of sporadic AD. The enzyme cytochrome c oxidase (COX), which makes up part of the mitochondrial electron transport chain (ETC), is present in normal amounts in AD patients; however, the catalytic activity of this enzyme in AD patients and in the brains of AD patients at autopsy has been found to be abnormally low (Parker et al., Neurology 44:1086-1090, 1994). This suggests that the COX in AD patients is defective, leading to decreased catalytic activity that in some fashion causes or contributes to the symptoms that are characteristic of AD.
One hallmark pathology of AD is the death of selected neuronal populations in discrete regions of the brain. Cell death in AD is presumed to be apoptotic because signs of cell death are observed whereas indicators of active gliosis and necrosis are not (Smale et al., Exp. Neurolog. 133:225-230, 1995; Cotman et al., Molec. Neurobiol. 10:19-45, 1995). The consequences of cell death in AD, neuronal and synaptic loss, are closely associated with the clinical diagnosis of AD and are highly correlated with the degree of dementia in AD (DeKosky et al., Ann. Neurology 27:457-464, 1990).
Indeed, focal defects in energy metabolism in the mitochondria, with accompanying increases in oxidative stress, may be associated with AD. It is well-established that energy metabolism is impaired in AD brain (Palmer et al., Brain Res. 645:338-342, 1994; Pappolla et al., Am. J. Pathol. 140:621-628, 1992; Jeandel et al., Gerontol. 35:275, 1989; Balazs et al., Neurochem. Res. 19:1131-1137, 1994; Mecocci et al., Ann. Neurol. 36:747-751, 1994; Gsell et al., J. Neurochem. 64:1216-1223, 1995). For example, regionally specific deficits in energy metabolism in AD brains have been reported in a number of positron emission tomography studies (Kuhl, et al., J. Cereb. Blood Flow Metab. 7:S406, 1987; Grady, et al., J. Clin. Exp. Neuropsychol. 10:576-596, 1988; Haxby et al., Arch. Neurol 47:753-760, 1990; Azari et al., J. Cereb. Blood Flow Metab. 13:438-447, 1993). Metabolic defects in the temporoparietal neocortex of AD patients apparently presage cognitive decline by several years. Skin fibroblasts from AD patients display decreased glucose utilization and increased oxidation of glucose, leading to the formation of glycosylation end products (Yan et al., Proc. Nat. Acad. Sci. USA 91:7787-7791, 1994). Cortical tissue from postmortem AD brain shows decreased activity of the mitochondrial enzymes pyruvate dehydrogenase (Sheu et al., Ann. Neurol. 17:444-449, 1985) and xcex1-ketoglutarate dehydrogenase (Mastrogiacomo et al., J. Neurochem. 6:2007-2014, 1994), which are both key enzymes in energy metabolism. Functional magnetic resonance spectroscopy studies have shown increased levels of inorganic phosphate relative to phosphocreatine in AD brain, suggesting an accumulation of precursors that arises from decreased ATP production by mitochondria (Pettegrew et al., Neurobiol Of Aging 15:117-132, 1994; Pettigrew et al., Neurobiol. Of Aging 16:973-975, 1995).
Signs of oxidative injury also are prominent features of AD pathology, and reactive oxygen species (ROS) are critical mediators of neuronal degeneration. Indeed, studies at autopsy show that markers of protein, DNA and lipid peroxidation are increased in AD brain, probably as a result of increased ROS production secondary to mitochondrial dysfunction (Palmer et al., Brain Res. 645:338-342, 1994; Pappolla et al., Am. J. Pathol. 140:621-628, 1992; Jeandel et al., Gerontol. 35:275-282, 1989; Balazs et al., Arch. Neurol. 4:864, 1994; Mecocci et al., Ann. Neurol. 36:747-751, 1994; Smith et al., Proc. Nat. Acad. Sci. USA 88:10540-10543, 1991). In hippocampal tissue from AD but not from controls, carbonyl formation indicative of protein oxidation is increased in neuronal cytoplasm, and nuclei of neurons and glia (Smith et al., Nature 382:120-121, 1996). Neurofibrillary tangles also appear to be prominent sites of protein oxidation (Schweers et al., Proc. Nat. Acad. Sci. USA 92:8463, 1995; Blass et al., Arch. Neurol. 4:864, 1990). Under stressed and non-stressed conditions incubation of cortical tissue from AD brains taken at autopsy demonstrate increased free radical production relative to non-AD controls. In addition, the activities of critical antioxidant enzymes, particularly catalase, are reduced in AD (Gsell et al., J. Neurochem. 64:1216-1223, 1995), suggesting that the AD brain is vulnerable to increased ROS production. Thus, oxidative stress may contribute significantly to the pathology of mitochondria associated diseases such as AD, where mitochondrial dysfunction and/or elevated ROS may be present.
Accordingly, there is a need for compounds, compositions and methods that limit or prevent damage to organelles, cells and tissues initiated by various consequences of mitochondrial dysfunction. In particular, because mitochondria are essential organelles for producing metabolic energy, agents that inhibit the production of, and/or protect mitochondria and cells against, ROS and other sources of injury would be especially useful. Such agents would be suitable for the treatment of degenerative diseases, including mitochondria associated diseases. The present invention fulfills these needs and provides other related advantages.
Briefly stated, the present invention is directed to the treatment of mitochondria associated diseases by administration to a warm-blooded animal in need thereof an effective amount of a mitochondria protecting agent having one of the following general structures (I) through (IV): 
wherein X1, X2, X3, X4, Y1, Y2, Y3, Y4, Z1, Z2, Z3, W1, W2, W3, A1, R1, R2, R3 and R4 are as identified in the following detailed description.
The compounds of this invention have activity over a wide range of mitochondria associated diseases, including (but not limited to) Alzheimer""s Disease, diabetes mellitus, Parkinson""s Disease, neuronal and cardiac ischemia, Huntington""s disease and other related polyglutamine diseases (spinalbulbar muscular atrophy, Machado-Joseph disease (SCA-3), dentatorubro-pallidoluysian atrophy (DRPLA) and spinocerebellar ataxias 1, 2 and 6), dystonia, Leber""s hereditary optic neuropathy, schizophrenia, and myodegenerative disorders such as xe2x80x9cmitochondrial encephalopathy, lactic acidosis, and strokexe2x80x9d (MELAS), and xe2x80x9cmyoclonic epilepsy ragged red fiber syndromexe2x80x9d (MERRF).
Accordingly, this invention is also directed to method of treating a mitochondira associated disease by administration of an pharmaceutically effective amount of a mitochondria protecting agent to a warm-blooded animal in need thereof, as well as to pharmaceutical compositions containing a mitochondria protecting agent of this invention in combination with a pharmaceutically acceptable carrier or diluent.
These and other aspects of the present invention will become evident upon reference to the following detailed description and attached drawings. To that end, various references are set forth herein which describe in more detail certain aspects of this invention, and are each incorporated by reference in their entirety.